1. Field of the Invention
The present invention relates to a method of and apparatus for selecting a transmission channel in a private or personal wireless telecommunications system including a radio base station and a mobile terminal communicable with the former.
2. Description of the Background Art
In a conventional radio telecommunications system, a base station provided in a cell is adapted to assign to mobile stations in that cell, channels whose frequencies differ from the frequencies of channels available to base stations included in contiguous cells, thereby preventing interference between the base stations.
However, the base stations included in a private radio telecommunications system must endure the following conditions:
(1) To a base station, the same channel bands are available to the base stations contiguous thereto;
(2) It cannot be examined which radio waves are transmitted by the base stations;
(3) The information about which channels are now being used cannot be transferred between the base stations; and
(4) Since the mobile stations are not adapted to continuously emit a radiowave, the failure to detect the radiowave from a mobile station, that is, the absence of the corresponding radiowave received by the base station, does not always mean that the channel is not used by another base station.
The foregoing presents a problem that it is difficult for a base station in a private wireless telecommunications system to select in the same channel band a channel different from the channels being used by the contiguous base stations to prevent interference from the latter.
In a high-rise, multiunit dwelling, in particular, a lot of private telecommunications systems may often be installed in which each apartment is provided with a private base station (mother unit) and its mobile stations (daughter units) in the horizontal and vertical spaces. Accordingly, it grows increasingly difficult to carry out quick and positive radio communications in such a space in which many base stations are present adjacent to each other.